Thanks Marine, you're of great help
Now the choice came down to one of these wires:
a) 24-6337-0027 Sn63Pb37 0.75mm flux core size 66 RA
b) 24-6337-9710 Sn63Pb37 0.75mm flux core size 66 RMA
c) 24-6337-9713 Sn63Pb37 0.75mm flux core size 58 RMA
(no other core sizes exist in the last catalog of the RA and RMA types)
d) 14-6337-0031 Sn63Pb37 0.75mm NO flux core
and to one of these flux-pens:
a) 83-1018-0186 186-18 RMA No-Clean
b) 83-1000-0186 186 RMA No-Clean
What do you think it’s the best combination?